The present invention relates generally to a system for determining the electrical phase of a conductor and more particularly to a system that determines the electrical phase of a conductor with an open circuit condition in a multiphase electrical power line.
The generation of electrical power is generally performed in large centrally located plants. These power plants use a fuel, such as coal or natural gas, to generate heat to create steam. The steam then expands through a turbine causing the turbine to rotate. This rotation is transferred to an electrical generator that creates rotating magnetic fields that produce electricity through induction. This type of electrical power is known as alternating current. Electrical generators of this type are typically arranged to generate three electrical currents or “phases” that are arranged 120 degrees apart. These phases are typically designated as the “A”, “B”, and “C” phases.
Each of the electrical phases is transmitted on a separate conductor with a layer of insulation surrounding each of the conductors. The insulation allows the routing of the conductors together from the generation plant to the end users while keeping the conductors electrically isolated from each other. Unfortunately, due to a variety of factors, including new construction, network expansion, environmental effects, or abrasions and mechanical wear for example, an open circuit condition may occur. In some cases the insulation between the electrical phases may deteriorate causing an electrical fault. These type of faults may also be the result of other causes, such as lightening strikes, or trees falling across the power lines for example. When a gap is created in the insulation a dielectric breakdown may occur causing a phase-to-phase short. This type of failure releases of a large amount of energy damaging the conductors and may result in the conductor physically breaking causing an open circuit condition.
When an open circuit condition such as that described above occurs, personnel are dispatched by the utilities to repair or reconnect the conductors. In the case of a failure caused by a phase-to-phase short, the conductors may be split and it is difficult for the lineman to identify which conductor is associated with which electrical phase. Identification of the correct phase is important for the proper operation of the power system. The crossing of phases during repairs will result in having to re-work the splice and risk potential failures that could damage the conductors and other equipment in the electrical network.
Before any work can be performed on the conductors, the feeder circuit in the distribution network needs to be identified and protected (grounded) for work. The method of identifying the feeder circuit will depend on how the conductors were damaged. If only one of the conductors is broken, applying a tracing current to the two remaining conductors can identify the feeder circuit. This technique is effective because the remaining conductors provide a return path for the tracer current.
When the fault causes a break in all three conductors, the tracing current method will not be effective since there is no return path. In this case, a spear is applied to the cable shorting all three conductors. This creates a path for the tracing current so that the feeder can be identified. However, the phase of each cable cannot be identified with the spear in place.
Commonly, the identification of the phases and the repairs of the cables are performed by separate personnel: a Splicer who repairs and splices the conductors back together, and a phase identification crew. Separate personnel are used because the tracing method used for identifying the phase requires additional special training. Further, the phase identification crew needs to locate and travel to the transformers located on either side of the section having an open circuit condition. The transformers are grounded, isolating the section having an open circuit condition. The Splicer then prepares the conductors for splicing. The identification crew applies an audio frequency tracing tone to the conductors on the transformer side of the conductor and then travels back to the section having the open circuit condition. The phase identification crew uses the trace tone to identify and label the phase on each of the conductors. This is repeated for each set (3 conductors) of cable ends that need to be spliced. In the case of medium voltage transmission cables, the transformers are located a distance from the location of the failure. It is time consuming for the phase identification crew to travel, set up to enter an underground structure to perform the splice, and then perform the testing required to establish the phases. In addition, multiple trips may be required. This is performed for each set of cable ends (a minimum of two).
Once the conductors are labeled, the Splicer may complete the repair and splice the conductors on either side of the open circuit section back together. The power lines may then be re-energized and electrical service restored.
The process of identifying and repairing conductors in a three phase system is time consuming and expensive. Further, the above process of applying a tracing current is not feasible when an open circuit is encountered. While the existing processes and systems for identifying and repairing three phase conductors are suitable for their intended purposes, there still remains a need for improvements particularly regarding the reduction of the amount of time required to make repairs. Further improvements are also needed to increase the reliability of the splicing repairs to avoid the need to re-work the repair.